Bubble-proof construction method for box girder inner mold chamfer template cloth

Abstract

The application discloses a kind of box girder inner mould chamfer template cloth anti-bubble construction methods, it is related to box girder inner mould chamfer template cloth construction technical field, wherein, box girder inner mould chamfer template cloth anti-bubble construction method includes cleaning and repairing chamfer base surface;Lay three-layer composite structure air-permeable template cloth, air permeability is greater than or equal to 500L / (m 2 ·s);Using batten and sealant fixed template cloth;Layer thickness is 300-500mm;Joint use insert type and attached type vibrator, and use vacuum auxiliary exhaust;Cover moisture-retaining curing film curing for more than or equal to 7 days.The application is combined with special air-permeable template cloth and layered vibration exhaust process, effectively solves the technical problems that bubbles are difficult to discharge in chamfer part of box girder inner mould, surface quality is poor, improves the compactness and appearance quality of chamfer concrete.

Description

Technical Field

[0001] This invention relates to the field of construction technology for chamfered template fabric for box girder inner formwork, and particularly to an anti-air bubble construction method for chamfered template fabric for box girder inner formwork. Background Technology

[0002] With the widespread application of prestressed concrete box girders in bridge engineering, the chamfered area of ​​the inner formwork, as the junction area between the web, bottom slab, and top slab, has a decisive impact on the overall structural performance due to its concrete construction quality. This area has a complex geometry, typically exhibiting three-dimensional curved surface transition characteristics, and its internal reinforcement is highly dense. The flowability of the concrete is severely restricted during pouring, causing air to easily accumulate at the interface between the formwork and the concrete, especially in concealed locations such as the chamfer root. This air bubble accumulation forms surface defects such as honeycomb and pitting after the concrete hardens, significantly reducing the structural appearance quality and weakening the concrete's density and long-term durability, posing a hidden danger to the safe operation of the bridge structure.

[0003] Currently, traditional steel or wooden formwork is commonly used in engineering practice. Some projects attempt to apply release agents to the formwork surface to reduce adhesion, or lay ordinary canvas or other materials to improve air permeability; others rely on attached or immersion vibrators for vibration and air removal. However, traditional steel formwork, although smooth, is completely impermeable, preventing air from escaping from the concrete and causing air bubbles to accumulate in large quantities at the chamfer roots. Ordinary formwork fabric, while possessing some air permeability, has uneven pore distribution and excessively large pore sizes, leading to concrete slurry seepage and resulting in a rough and uneven surface. The application of vibrators in chamfer areas is extremely unsatisfactory. Due to the narrow space, immersion vibrators are difficult to operate deeply, and the vibration energy of attached vibrators is attenuated on complex curved surfaces, failing to completely eliminate tiny air bubbles near the formwork surface. More notably, existing technologies lack a systematic anti-bubble construction process. The processes of formwork treatment, concrete pouring, vibration and curing are disconnected and poorly connected. Quality control relies excessively on the subjective experience of construction personnel and lacks scientific and standardized process guidance. As a result, the problem of air bubbles in the chamfered part of the box girder inner formwork has not been effectively solved for a long time. Summary of the Invention

[0004] The main objective of this invention is to propose an anti-bubble construction method for the chamfering template cloth of the inner formwork of a box girder, which aims to effectively reduce bubble defects in the chamfering part of the inner formwork of the box girder and improve the surface quality of concrete and structural durability.

[0005] To achieve the above objectives, the present invention proposes an anti-air bubble construction method for the chamfered template fabric of the box girder inner formwork, the anti-air bubble construction method of the chamfered template fabric of the box girder inner formwork comprising: Clean the base surface of the chamfered part of the box girder inner formwork, repair and level the unevenness of the base surface, remove floating dust and keep the base surface dry; A breathable template fabric is laid on the surface of the substrate; wherein the breathable template fabric comprises an outer supporting mesh fabric, a middle breathable filter layer, and an inner hydrophilic nonwoven fabric, and the air permeability of the breathable template fabric is ≥500L / (m²). 2 •s), with a pore size distribution of 50~200μm, and when laid, it is smoothly spread from the bottom of the chamfered part of the inner mold of the box girder to both sides, with an overlap width ≥100mm; The edges of the breathable template fabric are sealed and fixed using pressure strips and sealant. The pressure strips are arranged along the chamfered contour line with a spacing of 300-500mm. The sealant is applied between the pressure strips and the breathable template fabric and at the overlap to ensure that the breathable template fabric is tightly bonded to the substrate surface without any air pockets. A layered pouring process is adopted, with the thickness of each layer controlled at 300-500mm, the interval between layers controlled at 30-60 minutes, the concrete slump controlled at 180-220mm, and the spread controlled at 500-600mm. After each layer of concrete is poured, a combination of immersion vibrator and attached vibrator is used for compaction. The immersion vibrator is inserted to a depth of 50-100mm from the breathable formwork fabric and the compaction time is 20-30 seconds. The attached vibrator is placed on the outside of the chamfered part of the inner formwork of the box girder, with a vibration frequency of 200-300Hz and a vibration time of 30-60 seconds. Then, a vacuum-assisted exhaust device is used to perform negative pressure suction on the chamfered part of the inner formwork of the box girder. The negative pressure value is controlled at -0.03 to -0.05MPa and the duration is 5-10 minutes. After the concrete has initially set, a moisturizing and curing film is covered on the outside of the breathable formwork cloth. A sealed moisturizing layer is formed between the moisturizing and curing film and the breathable formwork cloth. The curing time is ≥7 days. After demolding, the formwork cloth is removed, and the surface of the chamfered part of the box girder is inspected for bubble defects.

[0006] This invention addresses the technical problem of air bubbles in concrete being difficult to expel due to the complex geometry and dense reinforcement of the chamfered area of ​​the box girder inner formwork. The invention employs a systematic design from two dimensions: "constructing a breathable channel" and "enhancing the venting force." First, a three-layer composite breathable template fabric is selected as the breathable interface. Utilizing the synergistic effect of its outer supporting mesh fabric maintaining shape, the middle breathable filter layer with uniformly distributed micropores, and the inner hydrophilic non-woven fabric guiding slurry penetration, a stable physical channel for air bubble expulsion is provided, solving the problems of traditional steel formwork's lack of breathability and the uneven pore size of ordinary template fabric. Second, a layered pouring process is used to control the thickness of each pour. Combined with the vibration of an immersion vibrator and an attached vibrator, internal and external vibration waves are superimposed. Then, a vacuum-assisted venting device applies negative pressure suction, constructing a gradient venting system of "vibration venting and vacuum suction," enhancing the migration force of air bubbles from the concrete interior to the template interface. Finally, sealing and moisturizing curing ensure a closed-loop process, thereby achieving effective control of air bubbles in the chamfered area and a significant improvement in surface quality. Attached Figure Description

[0007] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0008] Figure 1 This is a schematic flowchart of an embodiment of the anti-bubble construction method for the chamfered template cloth of the box girder inner formwork provided by the present invention.

[0009] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0010] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0011] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0012] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0013] In the existing concrete construction of the chamfered areas of box girder inner formwork, the use of traditional steel or wooden formwork makes it difficult for air in the concrete to escape, easily leading to air bubble accumulation at the root of the chamfer and resulting in quality defects such as honeycomb and pitting. Ordinary formwork has uneven pore size, allowing concrete slurry to easily seep out. The vibration effect of the vibrator at the chamfered area is uneven, making it difficult to completely expel air bubbles near the formwork surface. Current technology lacks a systematic anti-air bubble construction process, and quality control relies on experience-based judgment, resulting in difficulty in expelling air bubbles and poor surface quality at the chamfered areas of the box girder inner formwork.

[0014] To address this technical problem, this invention proposes a method for preventing air bubbles in the chamfered template fabric of the inner formwork of a box girder.

[0015] Please see Figure 1 In one embodiment of the present invention, the method for preventing air bubbles in the chamfered template cloth of the box girder inner formwork includes: Step S10: Clean the base surface of the chamfered part of the box girder inner formwork, repair and level the unevenness of the base surface, sweep away the floating dust and keep the base surface dry. Step S20: Lay a breathable template fabric on the surface of the substrate; wherein the breathable template fabric includes an outer supporting mesh fabric, a middle breathable filter layer, and an inner hydrophilic nonwoven fabric, and the air permeability of the breathable template fabric is ≥500L / (m²). 2 •s), with a pore size distribution of 50~200μm, and when laid, it is smoothly spread from the bottom of the chamfered part of the inner mold of the box girder to both sides, with an overlap width ≥100mm; Step S30: Use pressure strips and sealant to seal and fix the edge of the breathable template fabric. The pressure strips are arranged along the chamfered contour line with a spacing of 300-500mm. The sealant is applied between the pressure strips and the breathable template fabric and at the overlap to ensure that the breathable template fabric is tightly bonded to the substrate surface without any air pockets. Step S40: A layered pouring process is adopted, with the thickness of each layer controlled at 300-500mm, the interval between layers controlled at 30-60 minutes, the concrete slump controlled at 180-220mm, and the spread controlled at 500-600mm. Step S50: After each layer of concrete is poured, a combination of an immersion vibrator and an attached vibrator is used for compaction. The immersion vibrator is inserted to a depth of 50-100mm from the breathable template cloth, and the compaction time is 20-30 seconds. The attached vibrator is placed on the outside of the chamfered part of the inner formwork of the box girder, with a vibration frequency of 200-300Hz and a vibration time of 30-60 seconds. Then, a vacuum-assisted exhaust device is used to perform negative pressure suction on the chamfered part of the inner formwork of the box girder, with the negative pressure value controlled at -0.03~-0.05MPa for a duration of 5-10 minutes. Step S60: After the concrete has initially set, cover the outside of the breathable formwork cloth with a moisturizing and curing film. A sealed moisturizing layer is formed between the moisturizing and curing film and the breathable formwork cloth. The curing time is ≥7 days. After demolding, remove the formwork cloth and check the surface of the chamfered part of the box girder for air bubble defects.

[0016] For ease of understanding, the following explains some key terms in this embodiment: The chamfered area of ​​the box girder inner formwork refers to the transition area formed at the junction of the web, bottom slab, and top slab of the prestressed concrete box girder inner formwork. Its geometry is typically an arc or a slope, and it is an area prone to air bubble accumulation during concrete pouring. The substrate surface refers to the surface of the box girder inner formwork that directly contacts the concrete; its flatness and cleanliness directly affect the surface quality of the concrete. The breathable formwork fabric is a flexible material with specific breathability properties used to cover the substrate surface, allowing air and excess moisture in the concrete to escape while preventing cement slurry loss. This breathable formwork fabric consists of a multi-layer structure, including an outer supporting mesh fabric, a middle breathable filter layer, and an inner hydrophilic non-woven fabric. These layers work together to achieve the functions of breathability, filtration, and prevention of slurry loss. The outer supporting mesh fabric is located on the outermost side of the breathable formwork fabric, and its main function is to provide structural support, enhance the overall strength and tensile properties of the formwork fabric, and ensure the shape stability of the formwork fabric during concrete pouring and vibration. The intermediate breathable filter layer is located between the outer supporting mesh and the inner hydrophilic nonwoven fabric. Its main function is to allow air and moisture to pass through while effectively filtering solid particles in the cement slurry, preventing slurry leakage, and maintaining a smooth concrete surface. The inner hydrophilic nonwoven fabric is located on the innermost side of the breathable formwork fabric, in direct contact with the concrete. Its hydrophilic properties help guide free water and air bubbles in the concrete to escape, while preventing the formwork fabric from sticking to the concrete surface, facilitating demolding. The pressure strip is a component used to fix the edges of the breathable formwork fabric, usually arranged along the chamfered contour line, and uses mechanical compression to firmly fix the formwork fabric to the substrate surface. The sealant is a material with adhesive and sealing properties, used to fill the gaps between the pressure strip and the breathable formwork fabric, as well as the overlaps of the formwork fabric, ensuring a tight seal between the formwork fabric and the substrate surface, preventing concrete slurry leakage from the gaps. Layered pouring refers to pouring concrete in layers, vibrating each layer after it reaches a certain thickness, and then pouring the next layer only after the previous layer has initially set. This ensures the density and uniformity of the concrete and facilitates the removal of air bubbles. An immersion vibrator is a device that inserts a vibrating component into the concrete to compact it through high-frequency vibration, causing internal air bubbles to rise and be expelled. An attached vibrator is a vibrating device installed on the outside of a formwork, transferring vibrational energy to the concrete through the formwork, helping to remove air bubbles near the formwork surface. A vacuum-assisted degassing device is a device that generates negative pressure to suck up air from the concrete, accelerating the removal of air bubbles from the interior and surface of the concrete and improving its density. A moisture-retaining curing film is a thin film material used to cover the concrete surface to maintain its moisture. By forming a sealed moisture-retaining layer, it prevents excessive evaporation of moisture from the concrete surface, promotes cement hydration, and reduces the formation of shrinkage cracks.

[0017] This embodiment provides a method for preventing air bubbles in the chamfered template fabric of the inner formwork of a box girder.

[0018] First, base treatment is performed. This step includes cleaning the substrate surface of the chamfered area of ​​the box girder inner formwork, repairing and leveling any unevenness or irregularities on the substrate surface to ensure a flatness deviation of ≤3mm / 2m, removing loose dust, and keeping the substrate surface dry. Specifically, the substrate surface can be cleaned mechanically or manually to remove attached loose materials, dust, or oil. Repairs to unevenness or irregularities can be done using filler materials, such as cement-based or resin-based materials, to fill holes and cracks, followed by scraping to achieve the required flatness. Loose dust can be removed using vacuum cleaners or high-pressure airflow, ensuring the substrate surface is dry before subsequent construction.

[0019] Next, the breathable template fabric is laid. The breathable template fabric is laid on the surface of the substrate. This breathable template fabric consists of an outer supporting mesh fabric, a middle breathable filter layer, and an inner hydrophilic nonwoven fabric. The air permeability of this breathable template fabric is ≥500L / (m²). 2 The pore size distribution is 50~200μm. During installation, it is smoothly laid out from the bottom of the chamfered portion of the box girder's inner formwork towards both sides, with an overlap width ≥100mm. As one implementation method, the breathable formwork fabric can be composed of multiple fiber materials, such as polyester fiber and polypropylene fiber, forming a multi-layer structure through needle punching, hot rolling, or weaving processes. Its breathability and pore size distribution can be achieved by adjusting the material ratio and production process. During installation, the formwork fabric can be cut to a size suitable for the chamfered shape, ensuring a tight fit with the substrate surface to avoid wrinkles or air bubbles.

[0020] Next, sealing and fixing are performed. The edges of the breathable template fabric are sealed and fixed using pressure strips and sealant. The pressure strips are arranged along the chamfered contour line, spaced 300-500mm apart. The sealant is applied between the pressure strips and the breathable template fabric, as well as at the overlaps, ensuring a tight, seamless fit between the breathable template fabric and the substrate surface. Specifically, the pressure strips can be made of metal or engineering plastic, with an L-shaped or T-shaped cross-section to provide sufficient clamping force. The pressure strips are fixed to the template with bolts or rivets, and are evenly distributed along the chamfered contour line. The sealant can be a material with good adhesion and durability, such as polyurethane or silicone sealant. It is applied evenly to the contact surfaces between the pressure strips and the template fabric, as well as at the overlaps of the template fabric, using a specialized tool to form a continuous sealing layer. After fixing, the fit between the template fabric and the substrate surface can be checked, and any hollow areas can be treated.

[0021] Subsequently, layered pouring is carried out. A layered pouring process is employed, with each layer's thickness controlled at 300–500 mm, the interval between layers controlled at 30–60 minutes, the concrete slump controlled at 180–220 mm, and the spread controlled at 500–600 mm. During layered pouring, concrete can be pumped or manually poured into the formwork, and the thickness of each layer is controlled using a ruler or laser rangefinder. The interval between layers needs to be adjusted according to the concrete's setting characteristics and ambient temperature to ensure good interlayer bonding. The concrete slump and spread can be tested on-site, and the concrete mix proportions can be fine-tuned based on the test results to meet construction requirements.

[0022] Further, layered vibration and air removal are performed. After each layer of concrete is poured, a combination of immersion vibrators and attached vibrators is used for compaction. The immersion vibrator is inserted 50-100mm into the permeable formwork fabric, and the vibration time is 20-30 seconds. The attached vibrator is placed on the outside of the chamfered area of ​​the box girder's inner formwork, with a vibration frequency of 200-300Hz and a vibration time of 30-60 seconds. Subsequently, a vacuum-assisted air removal device is used to apply negative pressure to the chamfered area of ​​the box girder's inner formwork, with the negative pressure value controlled at -0.03 to -0.05MPa, for a duration of 5-10 minutes. Different diameter models of immersion vibrators can be selected, and their insertion point spacing and vibration time need to be adjusted according to the density of the concrete. The attached vibrator can be installed at a specific position on the outside of the formwork, and by adjusting its vibration frequency and amplitude, the vibration energy can be effectively transferred to the concrete. The vacuum-assisted air removal device, through connection to the extraction pipeline and vacuum pump, applies negative pressure to the chamfered area, causing air bubbles inside and on the surface of the concrete to be expelled.

[0023] Finally, surface sealing and curing are performed. After the concrete has initially set, a moisture-retaining curing film is placed over the outside of the breathable formwork fabric, forming a sealed moisture-retaining layer between the film and the fabric. Curing time is ≥7 days. After demolding, the formwork fabric is removed, and the surface of the chamfered area of ​​the box girder is inspected for air bubble defects. The initial setting time of the concrete can be determined through on-site testing or experience. The moisture-retaining curing film can be made of materials with good moisture retention properties, such as polyethylene film or a special curing agent, tightly covering the outside of the formwork fabric and sealing the edges to create a stable humid and hot environment. After the curing period, the formwork and fabric can be removed, and the concrete surface can be visually and tactilely inspected to assess air bubble defects.

[0024] This application effectively solves the problems of air bubbles being difficult to expel and poor surface quality during concrete pouring at the chamfered corner of the box girder's inner formwork through a systematic construction method. This method significantly improves the density of the concrete and reduces air bubble accumulation at the chamfered corner by employing a systematic construction approach, including fine treatment of the substrate surface, laying and sealing a special breathable template fabric, layered pouring and combined vibration for air release, and vacuum-assisted suction. This avoids defects such as honeycomb and pitting, ensuring the surface quality and structural durability of the concrete at the chamfered corner of the box girder's inner formwork.

[0025] In an embodiment of the present invention, the steps of cleaning the substrate surface of the chamfered portion of the box girder inner formwork, repairing and leveling the unevenness and defects on the substrate surface, removing floating dust, and keeping the substrate surface dry include: Step S11: Fill the holes and cracks on the surface of the substrate with polymer repair mortar. The strength grade of the polymer repair mortar is greater than or equal to the strength grade of the substrate concrete. After repair, the surface flatness is checked with a 2m straightedge and the gap is ≤3mm. Step S12: Spray an interface agent onto the repaired and dried substrate surface. The interface agent is a cement-based penetrating crystallizing type or an epoxy type. The spray thickness is 0.5-1.0 mm. After spraying, cure for 4-6 hours until the surface is dry. Step S13: Visual inspection and manual inspection are combined to ensure that the substrate surface is free of floating dust, oil stains, and loose particles, and the moisture content is ≤8%.

[0026] In the defect repair process, holes and cracks on the substrate surface are filled with polymer repair mortar. Polymer repair mortar is a composite material composed of cement, fine aggregate, polymer emulsion, and additives. It possesses good bond strength, crack resistance, and durability, effectively repairing structural defects in concrete substrates. To ensure the strength of the repaired area is not lower than that of the original substrate, the strength grade of the selected polymer repair mortar should be no lower than that of the substrate concrete. After repair, a 2m straightedge is used to check the surface flatness, ensuring gaps are no greater than 3mm. This provides a flat and continuous base surface, preventing poor adhesion of the breathable formwork or the formation of air pockets due to localized unevenness.

[0027] In the interface treatment step, an interface agent is sprayed onto the repaired and dried substrate surface. The interface agent serves to enhance the adhesion between the substrate surface and subsequent materials (such as breathable formwork fabric or concrete) and to regulate the water absorption of the substrate surface. In this application, the interface agent can be either cement-based penetrating crystalline or epoxy-based. Cement-based penetrating crystalline interface agents can form insoluble crystals inside the concrete through a chemical reaction, blocking capillary pores and improving the density and impermeability of the concrete; epoxy-based interface agents, with their excellent bond strength and chemical corrosion resistance, provide a strong bond interface for subsequent layers. The spray thickness of the interface agent is controlled between 0.5 and 1.0 mm to ensure uniform coverage and the formation of an effective interface layer. After spraying, curing is required for 4 to 6 hours until surface dry, allowing the interface agent to fully cure and form a stable bond interface.

[0028] In the cleanliness inspection process, a combination of visual and tactile checks is used to ensure that the substrate surface is free of floating dust, oil stains, and loose particles, and that the moisture content does not exceed 8%. Floating dust, oil stains, and loose particles can form an isolation layer, severely weakening interfacial adhesion; excessive moisture content may affect the curing effect of the interface agent and lead to water vapor generation and bubble formation during subsequent concrete pouring. Strict cleanliness inspections can eliminate potential factors affecting adhesion and bubble formation at the source.

[0029] Through the above technical solutions, this application refines and standardizes the surface treatment of the substrate at the chamfered area of ​​the box girder inner formwork. The defect repair step ensures the physical integrity and smoothness of the substrate surface, eliminating structural defects that could lead to voids in the permeable formwork or the accumulation of air bubbles in the concrete. The interface treatment step, through the application of an interface agent, significantly improves the bonding performance between the substrate and the permeable formwork and subsequent concrete, while also regulating the water absorption of the substrate surface, effectively preventing excessive moisture loss from the concrete or the formation of shrinkage cracks at the interface. The cleanliness inspection step, as a key step in quality control, thoroughly eliminates various contaminants and excess moisture that affect the bonding effect and air bubble formation. Overall, these measures work synergistically to provide a solid foundation for the tight adhesion of the permeable formwork and the air bubble-free pouring of concrete, thereby significantly reducing air bubble defects on the concrete surface at the chamfered area of ​​the box girder inner formwork and improving the density, durability, and appearance quality of the concrete.

[0030] In an embodiment of the present invention, the step of laying a breathable template cloth on the substrate surface includes: Step S21: Select the breathable formwork fabric according to the concrete strength grade and the geometric dimensions of the chamfered part of the box girder inner formwork. For C30~C50 concrete, select a fabric with an air permeability of 500~800L / (m²). 2 For formwork fabric with a permeability of 800-1200 L / (m²), and for concrete with a permeability of C50 or higher, use a fabric with a permeability of 800-1200 L / (m²). 2For template fabric with a chamfer radius R < 50mm, needle-punched nonwoven fabric should be used; for R ≥ 50mm, woven mesh fabric should be used. Step S22: Cut the breathable template fabric according to the unfolded length and overlap requirements of the chamfered part of the box girder inner mold. The cut size is 10% to 15% longer than the actual laying size. Pre-cut radial openings at the chamfered corners with an opening depth ≤ 50 mm and an opening spacing of 100 to 150 mm. Step S23: Before laying, immerse the breathable template cloth in clean water for ≥10 minutes. After removing it, let it drain naturally until it stops dripping. The moisture content should be controlled between 50% and 70% to prevent the dry template cloth from absorbing moisture from the concrete and causing surface cracking.

[0031] The selection of formwork fabric aims to ensure optimal matching between the chosen breathable formwork fabric and the chamfered areas of the box girder inner formwork, considering different strength grades of concrete and their geometric shapes. Higher concrete strength grades typically require higher density, leading to increased demands on venting efficiency and the compressive strength of the formwork fabric. The geometric dimensions of the chamfered areas of the box girder inner formwork, particularly the chamfer radius, directly affect the flexibility and fit requirements of the formwork fabric. Specifically, permeability is a key indicator of the formwork fabric's venting capacity. For medium- and low-strength concrete (C30~C50), internal air bubbles are relatively few and easily expelled; a medium-permeability formwork fabric is sufficient, effectively venting air while preventing concrete paste loss. However, for high-strength concrete (above C50), the mix proportion is usually denser, making it more difficult to expel internal air bubbles. Therefore, a higher permeability formwork fabric is required to ensure efficient venting and prevent air bubble retention. The chamfer radius determines the adaptability of the formwork fabric at bending points. When the chamfer radius is small (R<50mm), the template fabric needs to have excellent flexibility to ensure it can tightly conform to the complex curved surface and avoid wrinkles or gaps. In this case, needle-punched nonwoven fabric, due to its loose fiber structure and non-directional nature, has good extensibility and flexibility, making it an ideal choice. When the chamfer radius is large (R≥50mm), the requirement for the flexibility of the template fabric is relatively reduced, but the requirements for strength and dimensional stability may be higher. In this case, woven mesh fabric, due to its stable structure and high strength, can better maintain its shape and size, making it suitable for larger chamfers.

[0032] The pre-cutting process ensures that the formwork fabric's dimensions precisely match the actual construction area, avoiding waste or laying difficulties due to insufficient or excessive size. The unfolded length refers to the actual length of the chamfered section after unfolding along its curved surface. Overlap requirements consider the overlapping portion between adjacent formwork fabrics to ensure continuity and sealing. Allowing a certain margin facilitates on-site adjustment and trimming, ensuring complete coverage of the required area during laying and providing sufficient overlap width for subsequent sealing and fixing, while avoiding the need for re-cutting or splicing due to insufficient size. Pre-cutting radial openings at the chamfered corners is a key measure to solve wrinkles and stress concentration issues when laying the formwork fabric on curved surfaces. These openings allow for localized adjustment and stretching of the formwork fabric during bending, achieving a smooth fit, eliminating voids and wrinkles, ensuring close contact between the formwork fabric and the substrate surface, and providing uniform venting channels for the concrete. Controlling the opening depth and spacing ensures a good fit without compromising the overall structural strength and venting function of the formwork fabric.

[0033] The purpose of the impregnation pretreatment step is to fully saturate the formwork fabric fibers with water. This can be achieved by completely immersing the formwork fabric in clean water and ensuring a sufficient soaking time to allow water to evenly penetrate every corner of the fabric. After impregnation, the formwork fabric needs to be drained of excess water until it is no longer dripping, but still retains a certain moisture content. This can be achieved by hanging it to air dry or by gently squeezing it, ensuring that there is no free water on the surface of the formwork fabric, but the internal fibers are still saturated with moisture. A moisture content of 50%–70% is an empirical value aimed at achieving the best pre-wetting effect, preventing the formwork fabric from becoming too dry while avoiding the introduction of excessive moisture that could affect the water-cement ratio of the concrete. When dry, breathable formwork fabric comes into contact with fresh concrete, it will rapidly absorb free water from the concrete, leading to a localized decrease in the water-cement ratio at the formwork-concrete interface. This causes the concrete to lose water too quickly, resulting in shrinkage cracks or reduced strength on the concrete surface, affecting the durability and appearance quality of the concrete. Pre-impregnation treatment can effectively avoid this problem.

[0034] Through the aforementioned technical solutions, the permeable formwork fabric is precisely selected based on the concrete strength grade and the geometric dimensions of the chamfered area of ​​the box girder's inner formwork during the laying process. This ensures that the permeability and flexibility of the formwork fabric are highly matched to the specific construction conditions, effectively improving venting efficiency and the fit of the formwork fabric. Simultaneously, the radial opening treatment at the corners during the pre-processing step significantly solves the problem of wrinkles and air bubbles that easily occur when laying the formwork fabric on complex curved surfaces, ensuring a tight fit between the formwork fabric and the substrate surface. Furthermore, the pre-immersion treatment before laying effectively prevents surface cracking caused by the dry formwork fabric absorbing moisture from the concrete, thus guaranteeing the surface quality and anti-bubble effect of the concrete from the source. These measures work together to enable the permeable formwork fabric to perform its venting function more efficiently and stably, significantly reducing bubble defects at the chamfered area of ​​the box girder's inner formwork, and improving the durability and aesthetics of the concrete structure.

[0035] In an embodiment of the present invention, the edges of the breathable template fabric are sealed and fixed using pressure strips and sealant. The pressure strips are arranged along the chamfered contour line with a spacing of 300-500 mm. The sealant is applied between the pressure strips and the breathable template fabric and at the overlaps. The steps to ensure that the breathable template fabric is tightly bonded to the substrate surface without any voids include: Step S31: Arrange the pressure strips symmetrically on both sides of the chamfered portion of the inner mold of the box girder; Step S32: Apply the sealant to the contact surface between the pressure strip and the breathable template fabric, the overlap of the breathable template fabric, and the edge sealing area; Step S33: After the pressure strip is fixed, the fit between the breathable template cloth and the substrate surface is checked by hand tapping or by infrared thermal imaging. If any hollow areas are found, the sealant is injected into them using a syringe.

[0036] The selection and arrangement of the pressure strips aims to provide uniform and stable clamping force to the breathable formwork fabric, ensuring a tight fit between its edges and the substrate surface, preventing displacement or warping during concrete pouring and vibration. The pressure strips can be made of materials with good rigidity and durability, such as aluminum alloy profiles or engineering plastics, and their cross-sectional shape can be designed as "L" or "T" shaped to provide effective support and clamping surface. The width of the pressure strips is typically controlled between 30 and 50 mm, and the thickness is 2 to 3 mm to ensure sufficient clamping area and structural strength. During arrangement, the pressure strips are symmetrically placed on both sides of the chamfered portion of the box girder's inner formwork. Their spacing can be adjusted according to the chamfer length and curvature; for example, a spacing of 500 to 600 mm can be used on straight sections, while a spacing of 300 to 400 mm can be appropriately increased on curved sections to ensure uniform and effective clamping action in all areas. In addition to the materials and shapes mentioned above, the pressure strip can also be made of stainless steel or high-strength composite materials, and can be designed with other cross sections such as U-shape or Z-shape, as long as it can meet the requirements for fixing and pressing the breathable template cloth.

[0037] In the step of applying the sealant, the sealant is used to fill the tiny gaps between the edge of the breathable template fabric and the substrate surface, as well as at the overlap of the template fabric, thereby forming a continuous and dense impermeable barrier. In this embodiment, a single-component polyurethane sealant or silicone sealant with good adhesion, elasticity, and durability can be selected. The sealant should be precisely applied to the contact surface between the pressure strip and the breathable template fabric, the overlap of the breathable template fabric, and all edge sealing areas. The width of the sealant strip is usually controlled at 10-15 mm, and the thickness at 3-5 mm, to ensure sufficient sealing effect and bonding strength. To ensure that the sealant can form an effective bond with the pressure strip and template fabric before curing, the installation of the pressure strip should be completed within 10-15 minutes after the sealant is applied. In addition, modified epoxy resin or butyl rubber sealant can also be selected according to specific engineering requirements and environmental conditions, and the application methods can include scraping, injection, or extrusion.

[0038] The steps of checking and correcting hollow areas are crucial for ensuring a tight bond between the breathable template fabric and the substrate surface. After the pressure strip is fixed, non-destructive methods such as manual tapping or infrared thermal imaging can be used to comprehensively check the adhesion between the breathable template fabric and the substrate surface. Manual tapping identifies hollow areas by listening to the echo, while infrared thermal imaging can visually display hollow areas through surface temperature differences. Once a hollow area is found, corrective measures should be taken immediately. Correction methods include using a syringe to precisely inject the sealant into the hollow area to fill it, or using a special pressure roller to roll the hollow area to remove trapped air and ensure a tight bond between the template fabric and the substrate surface. These inspection and correction measures aim to ensure that the adhesion rate between the breathable template fabric and the substrate surface reaches or exceeds 95%, thereby fundamentally eliminating the risk of concrete slurry leakage and air bubble accumulation caused by hollow areas.

[0039] Through the above technical solution, this application can effectively solve the problem of air bubble defects caused by inadequate sealing and fixing of the breathable template fabric. Specifically, by rationally selecting, determining the size, and precisely arranging the pressure strips, a stable and uniform clamping force can be provided to the breathable template fabric, ensuring close contact between the edges of the template fabric and the substrate surface from a physical perspective, laying a solid foundation for subsequent sealing work. Simultaneously, by using a specific type of sealant and precisely controlling its application position, width, and thickness, combined with the process requirement of completing the pressure strip installation before the sealant cures, a continuous, dense, and highly elastic sealing layer can be formed, effectively preventing concrete grout from leaking through gaps and preventing external air from entering, thereby maintaining the integrity of the negative pressure exhaust channel inside the breathable template fabric. Furthermore, by introducing a step for checking and correcting voids, potential gaps between the breathable template fabric and the substrate surface can be detected and eliminated in a timely manner, ensuring a high adhesion rate between the template fabric and the substrate surface, and eliminating the possibility of air bubbles accumulating in these gaps from the source. Therefore, this embodiment significantly improves the reliability and effectiveness of the sealing and fixing of the breathable template cloth, ensuring that the breathable template cloth can fully exert its ventilation and exhaust function, thereby greatly reducing the air bubble defects on the concrete surface of the inner formwork chamfer area of ​​the box girder, significantly improving the surface quality and durability of the concrete, and reducing the cost of later repairs.

[0040] In an embodiment of the present invention, a layered pouring process is adopted, with the thickness of each layer controlled at 300-500 mm, the interval between layers controlled at 30-60 minutes, the concrete slump controlled at 180-220 mm, and the spread controlled at 500-600 mm. The steps include: Step S41: Determine the layer thickness based on the steel reinforcement density and vibrator radius at the chamfered part of the box girder inner formwork. When the steel reinforcement spacing is ≥150mm, the layer thickness is 400-500mm; when the steel reinforcement spacing is <150mm, the layer thickness is 300-400mm. Before each layer is poured, the material is evenly distributed along the entire length of the chamfered part of the box girder inner formwork. Step S42: Before pouring each layer of concrete, test the slump using a slump cone and a spread cone. Control the slump deviation within ±10mm and the spread deviation within ±20mm. Step S43: The interlayer interval time is determined based on the air temperature and the initial setting time of the concrete. When the interval time exceeds 50% of the initial setting time, mortar with the same mix ratio is laid or an interface agent is applied between the layers, with an interlayer bonding thickness of 5-10mm.

[0041] Specifically, the layered casting process includes the following steps: The steps for controlling layer thickness are as follows: The layer thickness is determined based on the reinforcement density at the chamfered area of ​​the box girder's inner formwork and the vibrator's effective radius. When the reinforcement spacing is ≥150mm, the layer thickness can be controlled between 400 and 500mm; when the reinforcement spacing is <150mm, the layer thickness is controlled between 300 and 400mm. Before pouring each layer of concrete, the concrete is evenly distributed along the entire length of the chamfered area of ​​the box girder's inner formwork. The layered pouring process aims to avoid excessive pouring at once, which could lead to concrete segregation and bleeding, and to create favorable conditions for subsequent vibration compaction and air bubble removal. Controlling the layer thickness to 300-500mm is based on a comprehensive consideration of the vibrator's effective range and the reinforcement density at the chamfered area of ​​the box girder's inner formwork, ensuring that each layer of concrete is fully vibrated. This step, through precise control of the layer thickness, adapts to construction environments with different reinforcement densities. When the reinforcement spacing at the chamfered area of ​​the box girder's inner formwork is large, the concrete flowability is less restricted, and the vibrator's effective range is relatively large; therefore, thicker layers can be used to improve construction efficiency. Conversely, when the spacing between reinforcing bars is small, the fluidity of the concrete is limited, increasing the difficulty of vibration. In this case, using thinner layers is more conducive to the compaction of the concrete and the expulsion of air bubbles. The uniform distribution of concrete along the entire length of the chamfered part of the inner formwork of the box girder at the front of each layer of pouring is to ensure that the concrete is evenly distributed across the entire pouring surface, avoiding local accumulation or voids, thereby ensuring the uniformity and compaction of subsequent vibration.

[0042] The steps for real-time slump monitoring are as follows: Before pouring each layer of concrete, the slump of the concrete is tested using a slump cone and a spread cone. The slump deviation should be controlled within ±10mm, and the spread deviation should be controlled within ±20mm. If the test results exceed these ranges, the admixture dosage or water dosage needs to be adjusted promptly. Controlling the concrete slump to 180–220mm and the spread to 500–600mm aims to ensure good fluidity and workability, facilitating pouring and vibration, while reducing bleeding and providing favorable conditions for the smooth removal of air bubbles. This step ensures that the workability of the concrete is always at its optimal state through real-time and accurate monitoring. Using a combined slump cone and spread cone test allows for a more comprehensive assessment of the concrete's fluidity and cohesiveness, avoiding the limitations of a single indicator. Controlling the slump deviation to within ±10mm and the spread deviation to within ±20mm ensures stable concrete performance during pouring and vibration, reducing air bubble formation and retention caused by workability fluctuations. If test results exceed allowable ranges, timely adjustments to the admixture dosage or water volume can quickly correct concrete performance and ensure construction quality.

[0043] Interlayer treatment steps: The interlayer interval is determined based on the air temperature and the initial setting time of the concrete. When the interval exceeds 50% of the initial setting time, a mortar of the same mix ratio is laid or an interface agent is applied between the layers, with the interlayer bonding thickness controlled at 5-10mm to ensure the quality of interlayer bonding. An interlayer interval of 30-60 minutes aims to ensure that the lower layer of concrete, while possessing a certain load-bearing capacity but not yet fully set, forms a good integral bond with the upper layer, effectively preventing cold joints. This step aims to effectively solve the cold joint problem that may occur during layered pouring and ensure the integrity of the interlayer bond. The determination of the interlayer interval needs to comprehensively consider the site air temperature and the initial setting time of the concrete to avoid premature hardening of the lower layer. When the actual interval is long, exceeding 50% of the initial setting time, the surface of the lower layer of concrete may have already formed a certain strength, and directly pouring the upper layer of concrete at this time easily leads to cold joints. By laying a mortar of the same mix ratio or applying an interface agent between the layers, the surface of the lower layer of concrete can be effectively activated, enhancing the bond between the old and new concrete. The interlayer bonding thickness is controlled at 5-10mm, which can ensure sufficient bonding strength without adversely affecting the overall structure, thereby ensuring the quality of interlayer bonding and avoiding bubble accumulation or structural weakness caused by interlayer defects.

[0044] Through the aforementioned technical solutions, after completing the base treatment, laying of breathable formwork fabric, and sealing and fixing of the chamfered area of ​​the box girder inner formwork, this application further employs refined layered pouring control. This includes determining a reasonable pouring thickness based on the reinforcement density and vibrator radius, as well as strictly controlling the interlayer interval. This effectively avoids segregation and air bubble retention caused by excessively thick concrete pours at once, ensuring that each layer of concrete is fully vibrated and compacted, and promoting the smooth removal of air bubbles. Simultaneously, real-time monitoring and adjustment of the concrete slump and spread before each layer pour ensures the stability of concrete workability, significantly reducing air bubble formation caused by fluctuations in concrete properties. Furthermore, targeted interlayer treatment measures, such as laying mortar with the same mix ratio or applying an interface agent, effectively prevent cold joints, ensuring the integrity and strength of the interlayer bond. Overall, these synergistic measures significantly improve the compactness and surface quality of the concrete at the chamfered area of ​​the box girder inner formwork, greatly reducing the occurrence of air bubble defects, thereby improving the durability and aesthetics of the structure.

[0045] In an embodiment of the present invention, after each layer of concrete is poured, a combination of an immersion vibrator and an attached vibrator is used for compaction. The immersion vibrator is inserted to a depth of 50-100 mm from the breathable formwork fabric, and the compaction time is 20-30 seconds. The attached vibrator is positioned on the outside of the chamfered portion of the box girder inner formwork, with a vibration frequency of 200-300 Hz and a vibration time of 30-60 seconds. Subsequently, a vacuum-assisted exhaust device is used to perform negative pressure suction on the chamfered portion of the box girder inner formwork, with the negative pressure value controlled at -0.03 to -0.05 MPa for a duration of 5-10 minutes. The steps include: Step S51: Use an immersion vibrator with a diameter of 30-50mm, with an insertion point spacing of 400-600mm, arranged in a quincunx pattern, and control the insertion depth to 50-100mm from the breathable template cloth. Step S52: Install attached vibrators on the outer template of the chamfered part of the inner formwork of the box girder. Arrange 1 to 2 vibrators per linear meter. The vibration frequency is 200 to 300 Hz and the amplitude is 0.5 to 1.0 mm. First start the lower vibrator to vibrate for 30 seconds, and then start the upper vibrator to vibrate for 30 seconds to form a vibration wave transmission from bottom to top. Step S53: Pre-embed an air extraction pipe on the outer side of the chamfered part of the inner mold of the box girder. The diameter of the air extraction pipe is 20-30mm, and small holes of φ3-5mm are opened in the pipe wall with a hole spacing of 50-100mm. Cover it with a 200-mesh filter screen. After the casting is completed, connect a vacuum pump for suction. The negative pressure value is -0.03~-0.05MPa, the air extraction rate is 5-10L / min, and the duration is 5-10 minutes. Stop when no bubbles overflow from the air extraction bottle.

[0046] The step of controlling the parameters of the immersion vibrator aims to effectively remove air bubbles from the concrete while protecting the breathable formwork fabric by precisely controlling the use of the immersion vibrator. Specifically, an immersion vibrator with a diameter of 30-50mm is used. This size range provides sufficient vibration energy and is easy to operate in areas with dense reinforcement. The spacing between insertion points is controlled at 400-600mm in a staggered pattern. This arrangement ensures that the vibration waves evenly cover the entire pouring layer, avoiding blind spots. The insertion depth is strictly controlled at 50-100mm from the breathable formwork fabric. This distance is optimized to ensure that the vibrator effectively vibrates the concrete near the formwork fabric, causing air bubbles to rise, while avoiding direct contact or scraping of the formwork fabric by the vibrator, thus preventing damage to the formwork fabric and affecting its breathability and filtration function. The vibration time at each point is 20-30 seconds, until the concrete surface is covered with slurry and no longer sinks, indicating that the concrete has reached a sufficiently dense state and the internal air bubbles have been largely removed.

[0047] The attached vibratory compaction parameter control steps utilize external vibration to assist internal vibration, further improving air removal efficiency. Attached vibrators are installed on the outer formwork of the chamfered section of the box girder's inner mold. Their placement allows them to directly act on the formwork, transferring vibration energy to the concrete in close contact with it, helping to eliminate surface air bubbles. One to two attached vibrators are placed per linear meter to ensure continuous and uniform vibration coverage. The vibration frequency is controlled at 200–300 Hz, and the amplitude at 0.5–1.0 mm. These parameters generate high-frequency, low-amplitude vibration, effectively reducing the viscosity of the concrete and causing tiny air bubbles to detach from the concrete surface and rise to the surface. To achieve better air removal, a strategy is adopted: first, the lower vibrator vibrates for 30 seconds, then the upper vibrator vibrates for 30 seconds, forming a bottom-up vibration wave transmission. This layer-by-layer upward vibration method guides air bubbles upward along the formwork surface, preventing air bubbles from remaining inside or at the bottom of the concrete, thus more effectively removing them.

[0048] The vacuum-assisted venting step actively removes air bubbles and excess moisture from the concrete through negative pressure suction, further enhancing the anti-bubble effect. Extraction pipes are pre-embedded on the outer side of the chamfered area of ​​the box girder's inner formwork; these pipes serve as venting channels. The extraction pipes are 20-30mm in diameter, with φ3-5mm small holes spaced 50-100mm apart in the pipe wall, and are covered with a 200-mesh filter. The design of the small holes and filter is intended to allow air and a small amount of moisture to pass through while effectively preventing concrete particles from entering the extraction pipes and causing blockages. After pouring, the extraction pipes are connected to a vacuum pump for suction, with the negative pressure controlled at -0.03 to -0.05MPa. This negative pressure range generates sufficient suction force to expel free water and air bubbles from the concrete through the breathable formwork and extraction pipes, while avoiding excessive negative pressure damage to the concrete structure. The suction rate is controlled at 5-10L / min for 5-10 minutes, and the process is stopped when no more air bubbles overflow from the extraction bottle, ensuring that the air bubbles have been fully removed.

[0049] By combining and optimizing the parameters of immersion vibration, attached vibration, and vacuum-assisted degassing techniques through the above technical solution, a synergistic and efficient anti-bubble construction method is formed. The immersion vibrator generates vibration inside the concrete, causing deep air bubbles to rise to the surface; the attached vibrator provides external assistance, particularly targeting air bubbles near the formwork surface, and guides the bubbles upwards through bottom-up vibration waves; while the vacuum-assisted degassing device actively extracts rising air bubbles and excess moisture from the breathable formwork fabric through negative pressure suction. This multi-action mechanism significantly improves the efficiency of air bubble removal from both the inside and surface of the concrete, especially in complex areas prone to air bubble accumulation, such as the chamfered corners of the box girder inner formwork. It effectively reduces air bubble defects, improves the density and surface quality of the concrete, thereby enhancing the durability and aesthetics of the box girder structure. Simultaneously, precise control over the immersion vibration depth and the design of the extraction pipe effectively avoids damage to the breathable formwork fabric, ensuring smooth construction.

[0050] In an embodiment of the present invention, after the concrete has initially set, a moisturizing and curing film is covered on the outside of the breathable formwork fabric, forming a sealed moisturizing layer between the moisturizing and curing film and the breathable formwork fabric. The curing time is ≥7 days. After demolding, the formwork fabric is removed, and the steps for checking the surface of the chamfered part of the box girder include: Step S61: Simultaneously prepare samples at the pouring site and use a penetration resistance meter to determine the initial setting time of the concrete. When the initial setting penetration resistance reaches 3.5 MPa, it is determined that the concrete has entered the initial setting state, and at this time, the moist curing film is covered. Step S62: The curing film is made of polyethylene film or a curing agent, with a film thickness ≥0.05mm. When covering, it is spread out from the bottom of the chamfered part of the box girder to both sides, with an overlap width ≥100mm. The edges are sealed with tape or fixed with weights, and the relative humidity inside the film is ≥90%. Step S63: Arrange a temperature sensor inside the moisture-retaining curing film to monitor the core temperature and surface temperature of the concrete. When the core-to-surface temperature difference is greater than 20°C, take ventilation cooling or covering insulation measures to control the cooling rate to ≤10°C / day.

[0051] Specifically, in the initial setting time determination step, accurately judging the initial setting time of concrete is crucial for subsequent curing operations. Covering the curing film too early may damage the concrete surface; covering it too late may cause premature evaporation of surface moisture, affecting the hydration process. Therefore, this application proposes to simultaneously prepare samples from the same batch as the actual poured concrete at the pouring site and use a penetration resistance meter to monitor the samples in real time. The penetration resistance meter measures the depth to which a standard probe penetrates the concrete sample under a certain pressure, thus reflecting the degree of hardening of the concrete. When the measured penetration resistance reaches 3.5 MPa, it indicates that the concrete has reached the initial setting state. At this point, the concrete possesses a certain strength, can withstand minor external operations without damage, and the internal hydration reaction begins to accelerate, making it the optimal time to cover with a moisture-retaining curing film.

[0052] In the process of laying the moisturizing curing membrane, its purpose is to provide a sealed, high-humidity curing environment for the concrete, preventing moisture evaporation and ensuring the full hydration reaction of the cement. The curing membrane can be a polyethylene film or applied by spraying a curing agent. The polyethylene film should have sufficient thickness, for example, not less than 0.05 mm, to ensure its ability to block water vapor and its durability. During laying, it should start from the bottom of the chamfered area of ​​the box girder's inner formwork and smoothly unfold to both sides, ensuring complete coverage. There should be sufficient overlap between adjacent curing membranes, for example, not less than 100 mm, to prevent moisture loss through the overlap seams. The edges of the curing membrane should be sealed with tape or secured with weights to ensure a tight fit between the membrane and the concrete surface, avoiding gaps. These measures ensure that the relative humidity inside the membrane is maintained above 90%, providing sufficient moisture for concrete hydration.

[0053] In the process of temperature control and crack prevention, concrete releases a large amount of heat during hydration, causing the internal temperature to rise. If there is an excessive temperature difference between the concrete core and surface, it may trigger thermal stress, leading to cracks and affecting structural durability and appearance. To effectively control the temperature difference, temperature sensors can be placed inside the curing membrane to monitor the concrete core and surface temperatures in real time. When the temperature difference between the core and surface exceeds 20°C, appropriate temperature control measures should be taken immediately. For example, cooling can be achieved by turning on ventilation equipment or covering the outside of the curing membrane with insulation material to slow heat loss, thereby controlling the concrete cooling rate to no more than 10°C / day. Through precise temperature monitoring and timely intervention, cracks caused by thermal stress can be effectively avoided, ensuring the concrete quality of the chamfered areas of the box girder's inner formwork.

[0054] By employing the aforementioned technical solutions, the initial setting time of concrete is accurately determined, ensuring that the moisturizing curing film is applied at the optimal time. This avoids disturbing the concrete surface due to premature application or causing premature evaporation of moisture due to delayed application. Simultaneously, by specifying the laying method, overlap width, and edge sealing requirements of the moisturizing curing film in detail, a sealed, high-humidity curing environment is effectively constructed, significantly improving the hydration efficiency and surface density of the concrete. Furthermore, temperature sensors are introduced to monitor the core and surface temperature of the concrete in real time, and corresponding cooling or insulation measures are taken based on the temperature difference, effectively controlling the cooling rate of the concrete and thus preventing cracks caused by temperature stress. These refined curing measures, combined with the aforementioned anti-bubble construction method, fundamentally improve the overall quality of the concrete at the chamfered corners of the box girder, significantly reducing bubble defects and effectively preventing cracks, ensuring the safety and durability of the structure.

[0055] In an embodiment of the present invention, after the concrete has initially set, a moisturizing and curing film is covered on the outside of the breathable formwork fabric, forming a sealed moisturizing layer between the moisturizing and curing film and the breathable formwork fabric. The curing time is ≥7 days. After demolding, the formwork fabric is removed, and the bubble defects on the surface of the chamfered part of the box girder are checked, the anti-bubble construction method of the chamfered formwork fabric of the box girder further includes: Step S70: After the curing period is over, remove the template and the breathable template cloth. Use a combination of visual inspection, touch inspection and tapping inspection to check the surface bubble defects at the chamfer of the inner formwork of the box girder. Bubble diameter <5mm is a minor defect, 5-10mm is a general defect, and >10mm or dense bubbles are a serious defect. Step S80: Slight defects are smoothed with mortar of the same mix ratio; general defects are filled with polymer repair mortar; and severe defects are repaired with pressure grouting. The grouting material is epoxy resin or micro-expansion cement grout, and the grouting pressure is 0.2~0.5MPa. Step S90: After the repair is completed, apply a penetrating waterproofing agent or epoxy coating to the surface of the chamfered part of the inner mold of the box girder. The coating thickness is 0.3-0.5mm to enhance the surface density and impermeability.

[0056] The demolding inspection step aims to comprehensively assess the surface quality of the concrete at the chamfered area of ​​the box girder's inner formwork. After the curing period, after removing the formwork and the breathable formwork fabric, a detailed inspection is conducted using a combination of visual, tactile, and tapping methods to identify any potential air bubble defects on the surface. Visual inspection primarily detects visible air bubbles, pitting, etc.; tactile inspection assesses surface smoothness, roughness, and the presence of loose particles; tapping (e.g., gently tapping with a small hammer) helps determine the presence of internal defects such as hollow areas and delamination. Based on the diameter and density of the air bubbles, defects are categorized into minor defects (bubble diameter less than 5mm), general defects (bubble diameter 5-10mm), and severe defects (bubble diameter greater than 10mm or densely distributed bubbles). This classification provides a basis for subsequent targeted repairs. For example, for tiny air bubbles or internal voids that are difficult to detect visually, a high-resolution industrial endoscope can be used for auxiliary inspection to ensure comprehensive defect identification.

[0057] The defect repair steps employ corresponding repair strategies for different types of air bubble defects discovered during formwork removal inspection. For minor defects, mortar with the same mix proportions as the original concrete is typically used for smoothing to restore surface flatness and ensure consistent appearance. For general defects, due to their larger size, which may affect local strength, polymer repair mortar is selected for filling. Polymer mortar has good adhesion, crack resistance, and durability, effectively repairing defects and forming a good bond with the original concrete. For severe defects, such as large-sized air bubbles or dense clusters of air bubbles, which may form through-holes or affect the structural bearing capacity, pressure grouting is used for repair. Epoxy resin or micro-expansion cement grout can be used as the grouting material. Epoxy resin has high strength, high adhesion, and excellent impermeability, making it suitable for structural repairs; micro-expansion cement grout can effectively fill voids and compensate for shrinkage, making it suitable for non-structural or large-area defects. The grouting pressure is controlled at 0.2~0.5MPa to ensure that the grouting material can fully penetrate and fill the defect while avoiding damage to the surrounding concrete.

[0058] Following defect repair, the concrete surface of the chamfered area of ​​the box girder's inner formwork undergoes further protective treatment. This is achieved by applying a penetrating waterproofing agent or an epoxy coating, aiming to enhance the density and impermeability of the concrete surface. Penetrating waterproofing agents (such as silanes and siloxanes) can penetrate deep into the concrete to form a hydrophobic layer, preventing moisture penetration without affecting the concrete's permeability. Epoxy coatings form a dense protective film on the surface, offering excellent wear resistance, corrosion resistance, and impermeability, making them particularly suitable for areas requiring high surface durability. The coating thickness is controlled between 0.3 and 0.5 mm to ensure effective protection without compromising the dimensional accuracy and appearance of the component. This protective layer effectively resists external environmental erosion, extending the service life of the concrete component.

[0059] Through the above technical solutions, this application further improves the control and assurance of the surface quality of the chamfered part of the box girder inner formwork in the later stage of construction, based on existing anti-bubble construction methods. Specifically, the demolding inspection step, through multi-dimensional and refined inspection methods, can comprehensively and accurately identify various bubble defects that may still exist under the previous preventive measures, avoiding potential quality problems caused by missed defects. On this basis, the defect repair step provides differentiated and professional repair solutions for defects of different severities. For example, pressure grouting is used to repair severe defects, which can effectively restore the density and integrity of the concrete, make up for the deficiencies of the previous preventive measures, and ensure the structural performance and appearance quality of the chamfered part. In addition, the surface protection step, by applying a penetrating waterproofing agent or epoxy coating to the repaired surface, significantly enhances the density and impermeability of the concrete surface, effectively resists the damage to the concrete caused by moisture erosion and environmental factors, thereby greatly improving the durability and long-term service performance of the chamfered part of the box girder inner formwork. Overall, these post-processing steps complement the earlier preventative measures, forming a complete quality control loop from prevention to detection to repair and protection, ensuring that the chamfered areas of the box girder's inner mold ultimately exhibit a high-quality, defect-free surface finish with excellent durability.

[0060] In an embodiment of the present invention, prior to the steps of employing a layered casting process, controlling the thickness of each layer to be 300–500 mm, controlling the interlayer interval to be 30–60 minutes, controlling the concrete slump to be 180–220 mm, and controlling the spread to be 500–600 mm, the method for preventing air bubbles in the chamfered formwork of the box girder further includes: Step S401: Use polycarboxylate high-performance water-reducing agent, and adjust the dosage according to 1.5% to 2.5% of the total amount of cementitious materials to reduce the water consumption of concrete by 15% to 20% while ensuring slump, thereby reducing air bubbles formed by free water. Step S402: Add organosilicon defoamer to concrete at a dosage of 0.01% to 0.03% to eliminate large air bubbles introduced during concrete mixing and transportation, while retaining small air bubbles to improve workability; Step S403: Add Grade II fly ash at a dosage of 20% to 30% to improve the workability of concrete, reduce bleeding and segregation. The spherical particle filling effect of fly ash can reduce the accumulation of air bubbles at the chamfered parts.

[0061] The step of optimizing the water-reducing agent dosage involves using polycarboxylate high-performance water-reducing agent. The dosage is adjusted according to 1.5% to 2.5% of the total cementitious materials, reducing water consumption by 15% to 20% while maintaining slump, thus reducing air bubbles formed by free water. Polycarboxylate high-performance water-reducing agent is a highly efficient concrete admixture that disperses cement particles and releases trapped water, thereby significantly reducing the water consumption of the mixture while maintaining concrete fluidity. This reduction in water consumption directly reduces the porosity formed by water evaporation after concrete hardening, fundamentally inhibiting air bubble formation. In practical applications, the dosage of water-reducing agent is usually determined through trial mixing based on the type and amount of cement and admixtures used, as well as the target slump and spread requirements. Strict metering accuracy is maintained to ensure thorough and uniform mixing with the concrete mixture.

[0062] The steps for optimizing defoamer dosage involve adding an organosilicon defoamer to concrete at a dosage of 0.01% to 0.03% to eliminate large air bubbles introduced during concrete mixing and transportation, while retaining small air bubbles to improve workability. Organosilicon defoamer is a chemical additive that effectively eliminates large air bubbles in concrete mixtures. Its mechanism of action is to reduce the surface tension of air bubbles, causing large air bubbles to break down or merge, thereby reducing large air bubbles generated during concrete mixing, transportation, and pouring due to mechanical action or the introduction of admixtures. Simultaneously, this defoamer retains small, uniformly distributed air bubbles in the concrete, which help improve workability without forming harmful surface bubble defects. Defoamers are typically added later in the concrete mixing process to ensure uniform dispersion throughout the mixture, and the dosage must be precisely controlled to ensure optimal defoaming effect and concrete performance.

[0063] The steps for optimizing fly ash admixture dosage include adding Grade II fly ash at a dosage of 20%–30%. This can improve the workability of concrete, reduce bleeding and segregation, and the spherical particle filling effect of fly ash can reduce air bubble accumulation in chamfered areas. As a mineral admixture, Grade II fly ash's spherical particles have a "ball-bead effect" and micro-aggregate filling effect. Adding it to concrete can significantly improve the workability of the mixture, increase fluidity, and reduce bleeding and segregation. The filling effect of fly ash makes the internal structure of concrete more compact, reducing porosity, especially in complex areas such as chamfered areas where air bubbles easily accumulate, effectively reducing air bubble retention and accumulation. The fly ash dosage should be optimized according to the concrete strength grade and performance requirements, ensuring that its fineness, loss on ignition, and other indicators meet relevant standards to fully realize its role in improving concrete performance.

[0064] Through the above technical solutions, this application systematically optimizes the concrete mix from the mix proportion source before concrete pouring. Specifically, by using a polycarboxylate high-performance water-reducing agent, the water content of the mix is ​​significantly reduced while ensuring the fluidity of the concrete. This reduces the porosity formed by the evaporation of free water during the concrete hardening process, fundamentally inhibiting the formation of air bubbles. Simultaneously, the addition of an organosilicon defoamer effectively eliminates large air bubbles generated during concrete mixing and transportation, preventing these large air bubbles from accumulating and forming defects at the chamfered edges. The retained micro-bubbles help improve the workability of the concrete. Furthermore, the addition of Grade II fly ash, utilizing its spherical particle filling effect and workability-improving properties, makes the concrete mix denser and more fluid, reducing bleeding and segregation, further reducing the retention and accumulation of air bubbles at the chamfered edges. These measures work synergistically to reduce the generation and retention of air bubbles from the inherent properties of the concrete mixture, providing a better concrete foundation for subsequent physical degassing and vibration, significantly improving the surface quality and density of the chamfered part of the box girder inner formwork, and effectively solving the air bubble problem caused by the inherent performance defects of the concrete.

[0065] In an embodiment of the present invention, prior to the steps of employing a layered casting process, controlling the thickness of each layer to be 300–500 mm, controlling the interlayer interval to be 30–60 minutes, controlling the concrete slump to be 180–220 mm, and controlling the spread to be 500–600 mm, the method for preventing air bubbles in the chamfered formwork of the box girder further includes: Step S310: The ambient temperature for concrete pouring is controlled between 5℃ and 30℃. When the temperature is >30℃, night construction or shading measures are adopted to reduce the concrete pouring temperature to ≤30℃ and reduce the expansion of air bubbles caused by temperature rise. Step S320: The relative humidity of the pouring environment is controlled at 50% to 80%. When the humidity is <50%, a spraying device is set up in the pouring area to increase the air humidity to more than 70% to prevent the concrete surface from evaporating too quickly and forming drying shrinkage cracks. Step S330: Control the wind speed in the pouring area to be ≤4. When the wind speed is high, set up windbreaks to prevent the concrete surface from losing water too quickly and the temperature from dropping suddenly due to excessive wind speed.

[0066] The temperature control step aims to maintain the ambient temperature of the concrete pouring environment within a suitable range of 5℃ to 30℃. When the air temperature exceeds 30℃, methods such as nighttime construction or shading measures can be adopted to lower the concrete's pouring temperature to no higher than 30℃. This effectively reduces the expansion of air bubbles inside the concrete due to temperature increases, thereby reducing the risk of air bubbles accumulating on the concrete surface. Specifically, nighttime construction utilizes the lower nighttime temperatures, naturally lowering the ambient temperature; shading measures reduce the heating of the concrete surface and the environment by blocking direct sunlight, helping to maintain a lower construction temperature. Furthermore, the pouring temperature of the concrete can be further controlled by pre-cooling the concrete raw materials (such as aggregates and mixing water) or adding ice during the concrete mixing process, ensuring that it is poured within the optimal temperature range.

[0067] The humidity control steps aim to maintain the relative humidity of the pouring environment between 50% and 80%. When the relative humidity is below 50%, a spray system can be installed in the pouring area to increase the air humidity to above 70%. This measure effectively prevents excessively rapid evaporation of moisture from the concrete surface, thus avoiding plastic shrinkage cracks caused by rapid surface water loss. Specifically, the spray system typically uses fine mist nozzles to evenly spray water mist into the air surrounding the pouring area, rather than directly onto the concrete surface, to avoid altering the water-cement ratio. By increasing the ambient humidity, the evaporation rate of the concrete surface can be slowed down, providing a more stable humid environment for the normal setting and hardening of the concrete, thereby reducing the occurrence of surface defects.

[0068] The wind speed control procedure aims to ensure that the wind speed in the pouring area does not exceed level 4 (i.e., 5.5 m / s). When the wind speed is high, windbreaks can be installed. This measure can effectively prevent excessive wind speed from causing rapid moisture loss and a sudden drop in temperature from the concrete surface. Specifically, windbreaks can be constructed using materials such as windproof netting, canvas, or temporary wall panels, and their height and arrangement should effectively block or reduce the impact of wind on the pouring area. By reducing wind speed, the evaporation of moisture from the concrete surface can be significantly reduced, avoiding surface cracking and plastic shrinkage caused by rapid water loss. It also prevents a sharp drop in concrete surface temperature due to wind cooling, thus providing a more stable environment for early curing of the concrete, which is beneficial for reducing the formation of air bubbles and improving surface quality.

[0069] Through the aforementioned environmental control measures, this application effectively addresses the adverse effects of external environmental factors on concrete construction quality. The temperature control step maintains the pouring environment temperature within a suitable range and takes measures to reduce the concrete's placement temperature at high temperatures, thereby inhibiting the expansion of air bubbles within the concrete due to temperature increases and reducing the accumulation and enlargement of bubbles at the chamfered areas. The humidity control step increases air humidity in low-humidity environments, effectively slowing down the rapid evaporation of moisture from the concrete surface and preventing the formation of plastic shrinkage cracks, which often become new channels for bubble exposure or formation. The wind speed control step reduces wind speed in the pouring area by setting up windbreaks, further reducing rapid moisture loss and temperature drops from the concrete surface, thus providing a stable microenvironment for normal concrete setting and hardening. These environmental control measures, in conjunction with core construction steps such as layered pouring and vibration venting, reduce the generation and retention of air bubbles at the source, protect the concrete surface quality, and ultimately significantly improve the anti-air bubble construction effect at the chamfered areas of the box girder inner formwork, ensuring the density and appearance quality of the concrete surface.

[0070] The following example will provide a more detailed explanation of the above technical solution: At the construction site of a box girder in a large bridge project, concrete needs to be poured at the chamfered areas of the inner formwork to ensure a surface free of air bubbles. Traditional construction methods often result in honeycombing and pitting at the chamfered areas, affecting structural durability and appearance. Therefore, the construction team decided to adopt an anti-air bubble construction method.

[0071] First, the substrate was treated before concrete pouring. Construction workers carefully cleaned the surface of the substrate at the chamfered corners of the box girder, using a high-pressure water gun to remove loose dust and particles. For holes and cracks on the substrate surface, such as holes approximately 10mm in diameter and micro-cracks approximately 200mm in length, polymer repair mortar with a strength grade no lower than the substrate concrete was used to fill them, and the surface was leveled with a trowel. After repair, a 2m straightedge was used to check the surface flatness, ensuring that all gaps were less than 3mm. After the repaired areas dried, a layer of cement-based penetrating crystalline interface agent with a thickness of approximately 0.8mm was evenly sprayed onto the entire substrate surface to enhance the bonding between the old and new concrete, and cured for 4 hours until the surface was dry. Finally, visual and tactile inspection confirmed that the substrate surface was free of loose dust, oil, and particles, and a moisture content tester was used to ensure that the moisture content was below 8%, creating a good foundation for the subsequent laying of the formwork fabric.

[0072] Next, the breathable formwork fabric was laid. Based on the design concrete strength grade of the box girder being C50 and the chamfer radius R being 60mm, the construction team selected a fabric with a permeability of approximately 900L / (m²). 2·s) woven mesh fabric is used as the breathable template fabric. This template fabric consists of an outer supporting mesh fabric, a middle breathable filter layer, and an inner hydrophilic non-woven fabric. Its pore size is distributed between 50 and 200 μm, which can effectively expel air from the concrete and prevent cement slurry leakage. Construction workers cut the template fabric into strips approximately 12% longer than the actual laying size according to the unfolded length and overlap requirements of the chamfered area. Radial openings approximately 40 mm deep and 120 mm apart are pre-cut at the chamfered corners to ensure a smooth fit. Before laying, the cut template fabric is soaked in clean water for 15 minutes, then allowed to drain naturally until no water drips, with a moisture content controlled at around 60% to prevent the dried template fabric from absorbing moisture from the concrete and causing surface cracking. Then, starting from the bottom of the chamfered area of ​​the box girder inner formwork, the template fabric is smoothly laid out to both sides, with the overlap width strictly controlled at over 100 mm to ensure the entire chamfered area is completely covered by the template fabric.

[0073] Next, sealing and fixing are performed. To ensure a tight, seamless fit between the breathable template fabric and the substrate surface, the installers used aluminum alloy L-shaped pressure strips and single-component polyurethane sealant for fixation. The pressure strips are 40mm wide and 2.5mm thick, symmetrically arranged along both sides of the chamfer contour line. Due to the long chamfer length, the spacing between the pressure strips on straight sections is set to 550mm, and the spacing on curved sections is set to 350mm. A layer of polyurethane sealant, approximately 12mm wide and 4mm thick, is evenly applied to the contact surface between the pressure strip and the breathable template fabric, as well as at the overlap and edge sealing areas of the template fabric. Within 10 minutes of applying the sealant, the pressure strips are quickly installed and fixed to ensure effective adhesion before the sealant cures. After the pressure strips are fixed, the installers use a combination of manual tapping and infrared thermal imaging to thoroughly inspect the adhesion between the template fabric and the substrate surface. When a hollow area with a diameter of approximately 30mm is found, immediately fill it with sealant using a syringe, or roll it with a special roller to remove air bubbles, ultimately ensuring that the adhesion rate between the formwork fabric and the substrate reaches over 95%. This sealing and fixing method effectively prevents concrete grout from leaking from the edges or overlaps, and ensures that the ventilation and air release functions of the breathable formwork fabric can be fully utilized.

[0074] Next, layered pouring was carried out. Before pouring the concrete, the construction team optimized the concrete mix proportions. A polycarboxylate superplasticizer, at 2% of the total cementitious materials, was used, reducing water consumption by approximately 18% while maintaining slump, thus reducing air bubbles formed by free water. Simultaneously, 0.02% silicone defoamer was added to eliminate large air bubbles introduced during mixing and transportation. Furthermore, 25% Class II fly ash was added, improving the workability of the concrete, reducing bleeding and segregation, and the spherical particle filling effect of fly ash also helped reduce air bubble accumulation at the chamfered edges. The pouring environment was controlled at 20℃, relative humidity at 75%, and wind speed below level 3, providing a stable environment for concrete pouring.

[0075] The construction employs a layered pouring process, with each layer's thickness controlled between 300 and 500 mm. Based on the reinforcement density at the chamfered section of the box girder's inner formwork (reinforcement spacing approximately 120 mm), the thickness of each layer is determined to be 350 mm. Before each layer is poured, the concrete is evenly distributed along the entire length of the chamfered section of the box girder's inner formwork. Before each layer of concrete is poured, the slump is monitored in real-time using a slump cone and a spread cone to ensure the slump is controlled within 180–220 mm (deviation within ±10 mm) and the spread is controlled within 500–600 mm (deviation within ±20 mm). If these ranges are exceeded, the admixture dosage or water content is adjusted promptly. The interlayer interval is controlled at 45 minutes to ensure sufficient load-bearing capacity of the lower concrete layer while allowing the upper concrete layer to form a good integral bond with the lower layer. When the interval approaches 50% of the initial setting time of the concrete, a layer of mortar with the same mix proportion, approximately 8 mm thick, is laid between layers to ensure good interlayer bonding. This layered pouring method, combined with optimized concrete mix proportions and environmental control, effectively reduces the generation and accumulation of air bubbles inside the concrete.

[0076] Subsequently, layered vibration and air removal are performed. Immediately after each layer of concrete is poured, a combination of immersion vibrators and attached vibrators is used for compaction. The immersion vibrators are 40mm in diameter, with insertion points spaced 500mm apart in a staggered pattern. The insertion depth is strictly controlled to be 50-100mm from the breathable formwork fabric to avoid direct contact and damage. Each point is vibrated for 25 seconds, until the concrete surface shows a layer of slurry and no longer settles. Simultaneously, attached vibrators are installed on the outer formwork of the chamfered corners of the box girder, one per linear meter, with a vibration frequency of 250Hz and an amplitude of 0.8mm. During vibration, the lower attached vibrator is started first for 30 seconds, followed by the upper attached vibrator for 30 seconds, creating an upward vibration wave that densifies the concrete and promotes the upward expulsion of air bubbles. After vibration, a vacuum-assisted air removal device is immediately connected. The device uses a 25mm diameter extraction pipe (with φ4mm holes spaced 80mm apart and covered with a 200-mesh filter) pre-embedded on the outside of the chamfered area of ​​the box girder's inner formwork to perform negative pressure suction. The negative pressure is controlled at -0.04MPa, the extraction rate is 8L / min, and the duration is 8 minutes. Degassing is confirmed by observing that no air bubbles overflow from the extraction bottle. This method, combining vibration and vacuum-assisted degassing, efficiently removes air bubbles from inside the concrete and near the formwork surface, significantly improving the concrete's density.

[0077] Finally, surface sealing and curing were carried out. Samples were prepared simultaneously at the pouring site, and the initial setting time of the concrete was measured using a penetration resistance meter. When the penetration resistance reached 3.5 MPa, the concrete was considered to have entered the initial setting state, at which point the moisturizing curing membrane was applied. The curing membrane was a 0.08 mm thick polyethylene film, spread outwards from the bottom of the chamfered corner of the box girder's inner formwork, with an overlap width greater than 100 mm. The edges were sealed with tape to ensure a tight fit between the curing membrane and the concrete surface, forming a sealed moisturizing layer, with the relative humidity inside the membrane maintained above 95%. Temperature sensors were placed inside the moisturizing curing membrane to monitor the core and surface temperatures of the concrete in real time. During curing, the core-to-surface temperature difference was consistently controlled within 20°C. By adjusting ventilation or covering with insulation measures as needed, the cooling rate was controlled to not exceed 10°C / day, effectively preventing the formation of temperature stress cracks. The curing period lasted for 7 days. After the curing period, the formwork and breathable formwork fabric were removed. After demolding, construction workers conducted a comprehensive inspection of the surface bubble defects at the chamfered area of ​​the box girder's inner formwork using a combination of visual, tactile, and tapping methods. The inspection results showed that the diameter of all surface bubbles was less than 5mm, classifying them as minor defects. These minor defects were smoothed using mortar with the same mix ratio. After repair, a layer of penetrating waterproofing agent with a thickness of approximately 0.4mm was applied to the surface of the chamfered area of ​​the box girder's inner formwork to enhance surface density and impermeability.

[0078] Through the aforementioned anti-air bubble construction method, the surface quality of the concrete at the chamfered area of ​​the box girder's inner formwork was significantly improved, essentially eliminating air bubble defects such as honeycomb and pitting commonly found in traditional construction. Compared to traditional steel formwork or ordinary formwork fabric, this method uses breathable formwork fabric combined with layered vibration and vacuum-assisted degassing, which can more thoroughly remove air from the concrete, preventing the accumulation of air bubbles at the chamfered root. Simultaneously, the systematic construction process and close coordination of each stage effectively solved the problem of relying on experience-based judgment for quality control in traditional methods, ensuring the stability and reliability of construction quality.

[0079] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent structural transformations made based on the technical concept of the present invention and the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of protection of the present invention.

Claims

1. A method for preventing air bubbles in the chamfering template fabric of a box girder inner formwork, characterized in that, The anti-bubble construction method for the chamfered template fabric of the box girder inner formwork includes: Clean the base surface of the chamfered part of the box girder inner formwork, repair and level the unevenness of the base surface, remove floating dust and keep the base surface dry; A breathable template fabric is laid on the surface of the substrate; wherein the breathable template fabric comprises an outer supporting mesh fabric, a middle breathable filter layer, and an inner hydrophilic nonwoven fabric, and the air permeability of the breathable template fabric is ≥500L / (m²). 2 •s), with a pore size distribution of 50~200μm, and when laid, it is smoothly spread from the bottom of the chamfered part of the inner mold of the box girder to both sides, with an overlap width ≥100mm; The edges of the breathable template fabric are sealed and fixed using pressure strips and sealant. The pressure strips are arranged along the chamfered contour line with a spacing of 300-500mm. The sealant is applied between the pressure strips and the breathable template fabric and at the overlap to ensure that the breathable template fabric is tightly bonded to the substrate surface without any air pockets. A layered pouring process is adopted, with the thickness of each layer controlled at 300-500mm, the interval between layers controlled at 30-60 minutes, the concrete slump controlled at 180-220mm, and the spread controlled at 500-600mm. After each layer of concrete is poured, a combination of immersion vibrator and attached vibrator is used for compaction. The immersion vibrator is inserted to a depth of 50-100mm from the breathable formwork fabric and the compaction time is 20-30 seconds. The attached vibrator is placed on the outside of the chamfered part of the inner formwork of the box girder, with a vibration frequency of 200-300Hz and a vibration time of 30-60 seconds. Then, a vacuum-assisted exhaust device is used to perform negative pressure suction on the chamfered part of the inner formwork of the box girder. The negative pressure value is controlled at -0.03~-0.05MPa and the duration is 5-10 minutes. After the concrete has initially set, a moisturizing and curing film is covered on the outside of the breathable formwork cloth. A sealed moisturizing layer is formed between the moisturizing and curing film and the breathable formwork cloth. The curing time is ≥7 days. After demolding, the formwork cloth is removed, and the surface of the chamfered part of the box girder is inspected for bubble defects.

2. The method for preventing air bubbles in the chamfered template fabric of the box girder inner formwork as described in claim 1, characterized in that, The steps of cleaning the base surface of the chamfered part of the box girder inner formwork, repairing and leveling the unevenness of the base surface, removing floating dust, and keeping the base surface dry include: The holes and cracks on the surface of the substrate are filled with polymer repair mortar. The strength grade of the polymer repair mortar is greater than or equal to the strength grade of the substrate concrete. After repair, the surface flatness is checked with a 2m straightedge and the gap is ≤3mm. After the repair is completed and the substrate surface is dried, an interface agent is sprayed onto it. The interface agent is cement-based penetrating crystallization type or epoxy type. The spray thickness is 0.5-1.0 mm. After spraying, it is cured for 4-6 hours until it is surface dry. A combination of visual and tactile inspections was used to ensure that the substrate surface was free of dust, oil, and loose particles, and that the moisture content was ≤8%.

3. The method for preventing air bubbles in the chamfered template fabric of the box girder inner formwork as described in claim 2, characterized in that, The step of laying a breathable template cloth on the substrate surface includes: The permeable formwork fabric is selected based on the concrete strength grade and the geometric dimensions of the chamfered portion of the box girder inner formwork. For C30~C50 concrete, a permeability of 500~800 L / (m²) is used. 2 For formwork fabric with a permeability of 800-1200 L / (m²), and for concrete with a permeability of C50 or higher, use a fabric with a permeability of 800-1200 L / (m²). 2 For template fabric with a chamfer radius R < 50mm, needle-punched nonwoven fabric should be used; for R ≥ 50mm, woven mesh fabric should be used. According to the unfolded length and overlap requirements of the chamfered part of the box girder inner mold, the breathable template cloth is cut. The cut size is 10% to 15% longer than the actual laying size. Radial openings are pre-cut at the chamfered corners, with an opening depth ≤ 50mm and an opening spacing of 100 to 150mm. Before laying, immerse the breathable template cloth in clean water for ≥10 minutes. After removing it, let it drain naturally until it stops dripping. The moisture content should be controlled between 50% and 70% to prevent the dry template cloth from absorbing moisture from the concrete and causing surface cracking.

4. The method for preventing air bubbles in the chamfered template fabric of the box girder inner formwork as described in claim 3, characterized in that, The steps of sealing and fixing the edges of the breathable template fabric with pressure strips and sealant, with the pressure strips arranged along the chamfered contour line at intervals of 300-500mm, and the sealant applied between the pressure strips and the breathable template fabric and at the overlaps, to ensure that the breathable template fabric adheres tightly to the substrate surface without any voids, include: The pressure strips are symmetrically arranged on both sides of the chamfered portion of the inner formwork of the box girder; Apply the sealant to the contact surface between the pressure strip and the breathable template fabric, the overlap of the breathable template fabric, and the sealed edge. After the pressure strip is fixed, the fit between the breathable template cloth and the substrate surface is checked by hand tapping or by infrared thermal imaging. If any hollow areas are found, the sealant is injected into them using a syringe.

5. The method for preventing air bubbles in the chamfered template fabric of the box girder inner formwork as described in claim 4, characterized in that, The process employs a layered pouring technique, with each layer controlled to a thickness of 300–500 mm, an interval of 30–60 minutes between layers, a concrete slump controlled to 180–220 mm, and a spread controlled to 500–600 mm. The steps include: The layer thickness is determined based on the steel reinforcement density and vibrator radius at the chamfered part of the box girder inner formwork. When the steel reinforcement spacing is ≥150mm, the layer thickness is 400-500mm; when the steel reinforcement spacing is <150mm, the layer thickness is 300-400mm. Before each layer is poured, the material is evenly distributed along the entire length of the chamfered part of the box girder inner formwork. The slump is tested before each layer of concrete is poured. A slump cone and a spread cone are used for testing. The slump deviation is controlled within ±10mm and the spread deviation is controlled within ±20mm. The interlayer interval is determined based on the air temperature and the initial setting time of the concrete. When the interval exceeds 50% of the initial setting time, mortar with the same mix ratio is laid or an interface agent is applied between the layers, with an interlayer bonding thickness of 5-10mm.

6. The method for preventing air bubbles in the chamfered template fabric of the box girder inner formwork as described in claim 5, characterized in that, After each layer of concrete is poured, a combination of immersion vibrator and attached vibrator is used for compaction. The immersion vibrator is inserted to a depth of 50-100mm from the breathable formwork fabric, and the compaction time is 20-30 seconds. The attached vibrator is placed on the outside of the chamfered part of the box girder inner formwork, with a vibration frequency of 200-300Hz and a vibration time of 30-60 seconds. Subsequently, a vacuum-assisted exhaust device is used to perform negative pressure suction on the chamfered part of the box girder inner formwork, with the negative pressure value controlled at -0.03~-0.05MPa for a duration of 5-10 minutes. The steps include: An immersion vibrator with a diameter of 30-50mm is used, with an insertion point spacing of 400-600mm, arranged in a quincunx pattern, and the insertion depth is controlled at 50-100mm from the breathable template cloth. An attached vibrator is installed on the outer template of the chamfered part of the inner formwork of the box girder. One to two vibrators are arranged per linear meter. The vibration frequency is 200 to 300 Hz and the amplitude is 0.5 to 1.0 mm. The lower vibrator is started first and vibrated for 30 seconds, and then the upper vibrator is started and vibrated for 30 seconds to form a vibration wave transmission from bottom to top. An air extraction pipe is pre-embedded on the outer side of the chamfered part of the inner formwork of the box girder. The diameter of the air extraction pipe is 20-30mm, and small holes of φ3-5mm are opened in the pipe wall with a hole spacing of 50-100mm. It is wrapped with a 200-mesh filter screen. After the casting is completed, a vacuum pump is connected for suction. The negative pressure value is -0.03~-0.05MPa, the air extraction rate is 5-10L / min, and the duration is 5-10 minutes. Stop when no bubbles overflow from the air extraction bottle.

7. The method for preventing air bubbles in the chamfered template fabric of the box girder inner formwork as described in claim 6, characterized in that, After the concrete has initially set, a moisturizing and curing film is placed on the outside of the breathable formwork fabric, forming a sealed moisturizing layer between the film and the fabric. The curing time is ≥7 days. After demolding, the formwork fabric is removed, and the steps for inspecting the surface of the chamfered area of ​​the box girder inner formwork for air bubbles include: Samples were made simultaneously at the pouring site, and the initial setting time of the concrete was measured using a penetration resistance meter. When the initial setting penetration resistance reached 3.5 MPa, the concrete was determined to have entered the initial setting state, and at this time, the moisturizing curing film was started to be covered. The curing film is made of polyethylene film or coated with a curing agent, with a film thickness of ≥0.05mm. When covering, it is spread out from the bottom of the chamfered part of the box girder to both sides, with an overlap width of ≥100mm. The edges are sealed with tape or fixed with weights, and the relative humidity inside the film is ≥90%. Temperature sensors are arranged inside the moisture-retaining curing film to monitor the core temperature and surface temperature of the concrete. When the core-to-surface temperature difference is greater than 20°C, ventilation or insulation measures are taken to control the cooling rate to ≤10°C / day.

8. The method for preventing air bubbles in the chamfered template fabric of the box girder inner formwork as described in any one of claims 1 to 7, characterized in that, After the concrete has initially set, a moisturizing and curing film is placed on the outside of the breathable formwork fabric, forming a sealed moisturizing layer between the moisturizing and curing film and the breathable formwork fabric. The curing time is ≥7 days. After demolding, the formwork fabric is removed, and the air bubble defects on the surface of the chamfered part of the box girder inner formwork are checked. The anti-air bubble construction method for the chamfered formwork fabric of the box girder inner formwork also includes: After the curing period, the template and the breathable template cloth are removed. Visual inspection, touch inspection and tapping inspection are used to check for surface bubble defects at the chamfer of the inner formwork of the box girder. Bubble diameter <5mm is a minor defect, 5-10mm is a general defect, and >10mm or dense bubbles are a serious defect. Minor defects are smoothed with mortar of the same mix ratio; general defects are filled with polymer repair mortar; and severe defects are repaired with pressure grouting. The grouting material is epoxy resin or micro-expansion cement grout, and the grouting pressure is 0.2~0.5MPa. After the repair is completed, a penetrating waterproofing agent or epoxy coating is applied to the surface of the chamfered part of the inner mold of the box girder. The coating thickness is 0.3 to 0.5 mm to enhance the surface density and impermeability.

9. The method for preventing air bubbles in the chamfered template fabric of the box girder inner formwork as described in any one of claims 1 to 7, characterized in that, Before adopting the layered pouring process, with each layer thickness controlled at 300-500mm, the interlayer interval controlled at 30-60 minutes, the concrete slump controlled at 180-220mm, and the spread controlled at 500-600mm, the anti-air bubble construction method for the chamfered template cloth of the box girder inner formwork further includes: Polycarboxylate high-performance water-reducing agent is used, and the dosage is adjusted according to 1.5% to 2.5% of the total amount of cementitious materials. This reduces the water consumption of concrete by 15% to 20% while ensuring slump, and reduces the air bubbles formed by free water. Adding organosilicon defoamer to concrete at a dosage of 0.01% to 0.03% eliminates large air bubbles introduced during concrete mixing and transportation, while retaining small air bubbles to improve workability. Adding Class II fly ash at a dosage of 20% to 30% can improve the workability of concrete, reduce bleeding and segregation, and the spherical particle filling effect of fly ash can reduce the accumulation of air bubbles at the chamfered parts.

10. The method for preventing air bubbles in the chamfered template fabric of the box girder inner formwork as described in any one of claims 1 to 7, characterized in that, Before adopting the layered pouring process, with each layer thickness controlled at 300-500mm, the interlayer interval controlled at 30-60 minutes, the concrete slump controlled at 180-220mm, and the spread controlled at 500-600mm, the anti-air bubble construction method for the chamfered template cloth of the box girder inner formwork further includes: The ambient temperature for concrete pouring should be controlled between 5℃ and 30℃. When the temperature is above 30℃, nighttime construction or shading measures should be adopted to reduce the concrete pouring temperature to ≤30℃ and reduce the expansion of air bubbles caused by temperature rise. The relative humidity of the pouring environment should be controlled between 50% and 80%. When the humidity is less than 50%, a spraying device should be set up in the pouring area to increase the air humidity to more than 70% to prevent the concrete surface from evaporating too quickly and forming drying shrinkage cracks. Control the wind speed in the pouring area to ≤4. When the wind speed is high, set up windbreaks to prevent the concrete surface from losing water too quickly and the temperature from dropping suddenly due to excessive wind speed.

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